Indomitable (adjective)
definition: incapable of being overcome, subdued,or vanquished; impossible to defeat or discourage

Synonyms: unconquerable, invincible,never-say-die, bulletproof,impregnable,unbeatable,unstoppable

Antonyms: superable, vincible, vulnerable, surmountable

Usage: A man of indomitable courage,it was said that the only thing he shied at was the sight of his blood,which was thick and of an unusual color.